The invention concerns a driving arrangement of a lifting gear and/or a traveling drive, particularly one having a pole-reversible rotary current motor with windings for at least two different drive speeds and with a pole switching element connecting the rotary current motor to a voltage supply in order to switch between the driving speeds of the motor.
In the state of the art, it is generally known how to employ electrical pole-reversible rotary-current induction motors for the horizontal or vertical movement of loads, for example, in traveling or lifting gears, whose direction of movement is reversible, in that two of the rotary current phases are exchanged with a reversing circuit. In addition, these rotary-current induction motors can have several windings, which have different numbers of pole pairs. Thus, the possibility exists of changing the rotary speed of the motor by a so-called pole reversal between the motor windings with the different numbers of pole pairs. The rotary speed ratio is then dictated by the pole number ratio of the motor windings. A customary solution for a pole reversing circuit involves switching contacts that are activated manually or with an electromagnetic drive. The latter are also known as contactors. In this case, the current involved in the power uptake of the motor is switched during both the reversal and the pole switching. All contacts of the contactors switch the full motor current during a change in direction of turning and/or the number of revolutions. Interruption of the current during inductive loads, which are produced here by the motor windings, results in sparking at the contacts. The spacing of the contacts must be chosen such that the spark is quickly extinguished and the contact itself withstands the resulting high temperatures without damage. It is necessary to design all control contactors for this type of operation. Reversing contactor and pole switching contactor have been dimensioned in accordance with the above-described mode of operation.
Known solutions, such as are described in the German application DE 39 07 853 A1, have two contactors with at least six power contacts for the reversal and at least one additional contactor with at least four power contacts for the pole switching. The space requirement and costs of the contactors increase out of proportion to the power being switched. Instead of control contactors, one can also use electronic semiconductor switches, although they, in turn, are more cost-intensive.
A switch combination with an on/off switch with a reversing switch in a common switch housing is already familiar from German application DE 40 26 376 A1, in which the reversing switch for the actuating of an electric motor is interlocked relative to the on/off switch. The purpose of this interlocking is to prevent the reversing switch for changing the direction of turning of the electric motor from being activated when the on/off switch is still in its on position and, thus, the electric motor is still being supplied with energy. The reversing switch can, therefore, only be operated in the current-free condition, which should prevent damage or destruction of the switching contacts of the reversing switch. This switch combination is used, for example, for the switching of an electric motor in a machine tool.
This mechanical solution naturally means that the switching times of the switch combination and, thus, its area of application are limited.
An air-conditioning unit is known from U.S. Pat. No. 5,041,775, whose blower is provided with a reversible alternating-current motor, whose drive speed can be changed between two speeds by means of a reversing element. A power switch is hooked up in front of the reversing element, by which the blower motor can be switched to the powerless state during the speed change.